Frist which seal in the temperature range of 600.degree.-1000.degree. C. represent an intermediate class of materials between the B.sub.2 O.sub.3 - or P.sub.2 O.sub.5 -based frits used for low temperature sealing of many commerical glass products and the diversifying frits used for high temperature joining of advanced ceramic, structural components. The low temperature frits are used at temperatures below 600.degree. C. for sealing products such as cathode ray tubes (CRT), light bulbs and the like. The diversifying high temperature frits are used at temperatures above 1,000.degree. C. to produce articles which may embody high temperature, fiber-reinforced, structural ceramics.
A very old product in the intermediate temperature range of sealing is a ZnO--B.sub.2 O.sub.3 --SiO.sub.2 frit. Another is a Li.sub.2 O-modified, ZnO--AI.sub.2 O.sub.3 --SiO.sub.2 frit designed for use between 900.degree.-1,000.degree. C. Frits that seal in the intermediate range of 600.degree.-800.degree. C. are important in many industrial applications. The need for such frits became evident through requests for sealant frits for solid oxide fuel cells (SOFC).